Institute of Electrical and Electronics Engineers (IEEE) 802.16m system supports TDD and FDD duplex modes, including Half-Frequency Division Duplex (H-FDD) MS operation, in accordance with the IEEE 802.16m system requirements document. Unless otherwise specified, the frame structure attributes and baseband processing are common for all duplex modes.
IEEE 802.16m system uses Orthogonal Frequency Division Multiple Access (OFDMA) as the multiple access scheme in the downlink and uplink. The OFDMA parameters for the IEEE 802.16m are specified as follows table 1.
TABLE 1Nominal578.751020ChannelBandwidth(MHz)Over-sampling28/258/78/728/2528/25FactorSampling5.681011.222.4Frequency(MHz)FFT Size5121024102410242048Sub-Carrier10.9375007.8125009.76562510.93750010.937500Spacing (kHz)Useful Symbol91.429128102.491.42991.429Time Tu (μs)CyclicSymbol102.857144115.2102.857102.857PrefixTime(CP)Tg =Ts⅛ Tu(μs)FDDNumber of OFDM48344348symbols per FrameIdle time (μs)62.85710446.4062.857TDDNumber of OFDM47334247symbols per FrameTTG + RTG (μs)165.714248161.6165.714CyclicSymbol97.143136108.897.14397.143PrefixTime(CP)Tg =Ts 1/16 Tu(μs)FDDNumber of OFDM51364551symbols per FrameIdle time (μs)45.7110410445.71TDDNumber of OFDM50354450symbols per FrameTTG + RTG (μs)142.853240212.8142.853CyclicSymbol114.286[TBD][TBD]114.286114.286PrefixTime(CP)Tg =Ts¼ Tu(μs)FDDNumber of OFDM43[TBD][TBD]43symbols per FrameIdle time (μs)85.694[TBD][TBD]85.694TDDNumber of OFDM42[TBD][TBD]42symbols per FrameTTG + RTG (μs)199.98[TBD][TBD]199.98
The IEEE 802.16m basic frame structure is illustrated in FIG. 1. Each 20 ms superframe is divided into four equally-sized 5 ms radio frames, data is transmitted to MS in superframe unit. When using the same OFDMA parameters as in Table 1 with the channel bandwidth of 5 MHz, 10 MHz, or 20 MHz, each 5 ms radio frame further consists of eight subframes. A subframe is assigned for either downlink (DL) or uplink (UL) transmission. There are three types of subframes: 1) the type-1 subframe which consists of six OFDMA symbols, 2) the type-2 subframe that consists of seven OFDMA symbols, and 3) the type-3 subframe which consists of five OFDMA symbols. Each 5 ms radio frame further consists of eight AAI subframes for G=⅛ and 1/16. With the channel bandwidth of 8.75 and 7 MHz, each 5 ms radio frame further consists of seven and six AAI subframes, respectively for G=⅛ and 1/16. In the case of G=¼, the number of AAI subframes per frame is one less than that of other Cyclic prefix (CP) lengths for each bandwidth case. Each subframe is consist of 5 to 8 symbols. A AAI subframe shall be assigned for either DL or UL transmission.
As above described, the basic frame structure is applied to FDD and TDD duplexing schemes, including H-FDD MS operation. The number of switching points in each radio frame in TDD systems is two, where a switching point is defined as a change of directionality, i.e., from DL to UL or from UL to DL.
When H-FDD MSs are included in an FDD system, the frame structure from the point of view of the H-FDD mobile station is similar to the TDD frame structure. However, the DL and UL transmissions occur in two separate frequency bands. The transmission gaps between DL and UL (and vice versa) are required to allow switching the Tx and Rx circuitry.
As shown in FIG. 1, a superframe header consists of four subframes. Data is transmitted to MS in superframe unit. H-FDD frame structure succeeds to existing superframe structure, MS need to receive SFH and Advanced-preamble (A-preamble) signal from BS. SFH is located at a first subframe of first frame in a superframe, A-preamble is located at a first subframe of second, third, and fourth frame in the superframe. More specifically, primary A-preamble is located at a first subframe of second, secondary A-preamble is located at a first subframe of third and fourth frame. Superframe header (SFH) is transmitted to MS in superframe unit (every 20 ms). A-Preamble is transmitted to MS in frame (every 5 ms). All the AAI H-FDD MSs should receive the SFH and A-Preamble.
Downlink HARQ and uplink HARQ timing problem is caused by applying existing H-FDD frame structure. That is, the number of UL subframes or DL subframes is varied when two and more superframes are considered. But, H-FDD based frame structure solution for the DL, UL HARQ timing problem is not proposed. Also, the relay frame structure for DL, UL HARQ timing is not proposed yet.